The present invention relates to continuous or semi-continuous casting apparatus of the direct chill type for casting metallic materials, particularly rectangular ingots of aluminum, comprising a mold cavity which has an open inlet for the filling of molten metal and an open outlet with water supply means for cooling of the metal. The mold cavity, at a position spaced from its inlet, is provided with a permeable ring for the supply of oil and/or gas, such that a layer of oil and/or gas is formed between the metal and the mold wall, whereby the metal is prevented from coming into contact with the mold wall before it solidifies.
It is previously known to supply oil or gas to the mold cavity in the above manner. For example, Norwegian patent application No. 830858 reveals a casting apparatus for ingots where gas and oil is supplied to the mold cavity via a graphite ring which is disposed in the mold wall close to the mold outlet.
Oil and gas is supplied to the graphite ring through separate bores in the outer mold wall e.g. in the form of a sleeve. By means of channels on the outer side of the ring which are connected to the bores in the sleeve, the oil and gas is distributed around the periphery of the ring.
To avoid oil and gas leakage between the ring and sleeve, it is necessary that the ring and sleeve be sealed tight to one another. Thus, the diameter of the graphite ring is machined to a size which is somewhat greater than the diameter of the sleeve. When mounting takes place, the sleeve is heated to expand so that the ring can be placed in its correct position within the sleeve. Further, upon cooling the sleeve will shrink, whereby sealing is achieved between the ring and sleeve. However, this will demand a very fine and accurate machining of the ring as well as the sleeve, and the smallest surface defect or scratch will result in leakage.
With the above demands regarding tolerances and surface roughness, it is obvious that this type of graphite ring is expensive to manufacture and use.
Besides, the above type of ring is hardly applicable for a casting apparatus producing rectangular ingots, primarily because the metal parts of the mold are machined by milling, and secondarily because the graphite "ring" has to have a rectangular configuration, i.e. the sides of the ring (frame) will be deflected inwardly so that it is impossible to use a force bit between the ring and the sleeve.